This important book contains the invited papers (plenary and review lectures, progress and special reports) presented at XX.ICPEAC, the Twentieth International Conference on the Physics of Electronic and Atomic Collisions. It highlights the current status of research in photonic, electronic and atomic collision physics, for which experimental studies increasingly rely on laser and synchrotron radiation and are more and more interrelated with other fields, such as molecular and chemical physics, surface science, quantum optics, and spectroscopy and formation of exotic atoms.